LeetCode 1461 | Check If a String Contains All Binary Codes of Size K

🚀 **LeetCode 1461 | Check If a String Contains All Binary Codes of Size K | Explained**

In this video, we solve **LeetCode Problem 1461** using an efficient **Sliding Window + HashSet approach**.

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🔍 **Problem Statement**
Given a binary string `s` and an integer `k`, we must check whether **all possible binary codes of length `k`** exist as substrings of `s`.

👉 Total possible binary codes of length `k` = **2^k**
Our task is to verify if every one of them appears in the string.

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💡 **Approach Used**

✅ Use a **Sliding Window** of size `k` to scan the string
✅ Extract each substring of length `k`
✅ Store unique substrings in a **HashSet**
✅ If the number of unique substrings equals `2^k`, return **true**
❌ Otherwise, return **false**

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🧠 **Key Concepts Covered**

✔ Sliding Window Technique
✔ Hashing for fast lookup
✔ Understanding binary combinations (`2^k`)
✔ Optimizing from brute force to linear time
✔ Interview-friendly pattern recognition

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📈 **Complexity Analysis**

⏱️ Time Complexity: **O(n)** — Single pass through the string
📦 Space Complexity: **O(2^k)** — To store unique binary codes

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📌 This problem is important for mastering:

* String pattern problems
* Bit manipulation thinking
* Efficient substring tracking
* FAANG-style interview questions

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